1. Field of the Invention
The present invention relates to a rotational angle detecting device, and, more particularly, to a rotational angle detecting device which is connected to a rotary member, such as a steering shaft of an automobile, and which outputs two or more detection signals which are in correspondence with the rotational angle and the rotational direction of the steering wheel in order to detect the rotational angle of the rotary member using these detection signals.
2. Description of the Related Art
Hitherto, a rotary sensor has been used to form a rotation detecting section. As an example of such a rotary sensor, the following rotary sensor will be described. (This rotary sensor will hereinafter be referred to as xe2x80x9cconventional rotary sensor.xe2x80x9d)
The conventional rotary sensor comprises a fixed base member, a rotor which can rotate with respect to the base member, and a rotation detecting section disposed between the base member and the rotor. The rotation detecting section outputs a sinusoidal first detection signal, a sinusoidal second detection signal, and a third detection signal. The first and second detection signals have constant amplitudes and the same periods, and are out of phase by xc2xc wavelength. The third detection signal has the same period in the entire rotational range of the rotor and increases linearly. When the rotary sensor is used, the rotor is connected to a rotary member such as a steering shaft of an automobile. Here, the rotation detecting section comprises first and second magnets, and first to third Hall elements. The first and second magnets are disposed at the base member. The first and second Hall elements are disposed at the rotor so as to oppose the first magnet at an angle of substantially 90 degrees. The third Hall element is disposed so as to oppose the second magnet.
In this structure, when the steering wheel is rotated in order to rotate the steering shaft connected to the steering wheel, the rotor connected to the steering shaft rotates, causing the rotation detecting section to generate the first to third detection signals which are in correspondence with the rotational angle and the rotational direction of the steering shaft.
The generated first to third detection signals are supplied to a controlling section installed in the automobile. Based on the supplied third detection signal, the controlling section detects the rotational direction and the rough rotational angle from the neutral position of the steering wheel (or the steering shaft). Similarly, based on the supplied first and second detection signals, the controlling section detects the very small rotational angle from the neutral position of the steering wheel (or the steering shaft). The detected rotational direction and rotational angles from the neutral position of the steering wheel (or the steering shaft) are supplied to a controller as detection information. Based on the supplied detection information, the controller carefully controls the traction and the suspension of the automobile.
FIG. 7 is a graph showing the relationship between the angle of rotation of the steering wheel and the output voltage of each of the first, second, and third detection signals.
In FIG. 7., reference numeral 71 denotes the first detection signal, reference numeral 72 denotes the second detection signal, and reference numeral 73 denotes the third detection signal. FIG. 7 shows the variations in the output voltages of the first to third detection signals 71 to 73 with respect to a rotational angle of zero degrees (that is, the neutral position) of the steering wheel, within a rotational angle range of from 0xc2x0 to +225xc2x0.
Here, the first detection signal 71 and the second detection signal 72 are sinusoidal, have the same amplitudes and periods, and are out of phase by xc2xc wavelength. For both of these signals 71 and 72, the voltages are 4.5 V at maximum amplitude, and 0.5 V at minimum amplitude. For the first detection signal 71, when the rotational angles are +67.5xc2x0 and +157.5xc2x0, the amplitude thereof is a minimum (voltage=0.5 V). For the second detection signal 72, when the rotational angles are 0xc2x0, +90.0xc2x0, and +180.0xc2x0, the amplitude thereof is a minimum (voltage=0.5 V). The third detection signal increases linearly from a rotational angle of 0xc2x0 to +225xc2x0, and has a voltage of 2.5 V when the rotational angle is 0xc2x0 and a voltage of 3.0 V when the rotational angle is +180xc2x0.
Hereunder, using the graph of FIG. 7, the detection of the rotational direction and rotational angle of the steering wheel carried out at the controlling section will be described.
First, when the controlling section is to detect the rotational direction of the steering wheel from the neutral position (which corresponds to an angle of rotation of 0xc2x0) of the steering wheel, it detects the rotational direction by the voltage value of the supplied third detection signal 73 which has been supplied. More specifically, when the voltage value of the third detection signal 73 is more than 2.5 V, the controlling section detects that the rotational direction of the steering wheel corresponds to one direction (that is, the positive rotational angle direction). On the other hand, when the voltage value of the third detection signal 73 is less than 2.5 V, the controlling section detects that the rotational direction of the steering wheel corresponds to the other direction (that is, the negative rotational angle direction).
Then, as shown in FIG. 7, the controlling section divides the entire rotational angle range of the steering wheel, such as a rotational angle range of 1440xc2x0 (xc2x1720xc2x0), into angle (such as 90xc2x0) divisions which correspond to one wavelength of each of the first detection signal 71 and the second detection signal 72. These divisions are represented as . . . , Nxe2x88x921, N, Nxe2x88x922, . . . Then, based on the voltage value of the supplied third detection signal 73, the controlling section detects a rough rotational angle which indicates to which angle division the rotational angle of the steering wheel corresponds. For example, if the controlling section detects that the voltage value of the third detection signal 73 is 2.8 V, the angle division N is detected as the angle division corresponding to this voltage value.
Thereafter, the controlling section determines a first voltage value V1 and a second voltage value V2 when the voltage values of the supplied first and second detection signals 71 and 72 are the same in the detected angle division N. Using the obtained first and second voltage values V1 and V2, one detection signal which has a voltage value outside the voltage range of the first and second voltage values V1 and V2, and the other detection signal which has a voltage value within the voltage range of the first and second voltage values V1 and V2 are determined.
After the determination, the controlling section determines whether the other detection signal whose voltage value lies within the voltage range of the first and second voltage values V1 and V2 is the first detection signal 71 or the second detection signal 72. At the same time, the controlling section determines whether the one detection signal whose voltage value lies outside the voltage range of the first and second voltage values V1 and V2 has a voltage value which is less than the first voltage value V1 or greater than the second voltage value V2, and whether the other detection signal whose voltage value lies within the voltage range of the first and second voltage values V1 and V2 exists in any one of four division portions of the one angle division N, that is, in any one of first to fourth angle division portions H1 to H4 of the one angle division N. Accordingly, by finding out whether the other detection signal exists in any one of the first to fourth angle division portions H1 to H4 of the one angle section N, the controlling section detects the very small rotational angle of the steering wheel.
Here, for the other detection signal whose voltage value lies within the voltage range of the first and second voltage values V1 and V2, the first angle division portion H1 corresponds to a rising (inclined) portion 71U where the first detection signal 71 rises linearly, the second angle division portion H2 corresponds to a rising (tilted) portion 72U where the second detection signal 72 rises linearly, the third angle division portion H3 corresponds to a falling (inclined) portion 71D where the first detection signal 71 falls linearly, and the fourth angle division portion H4 corresponds to a falling (inclined) portion 72D where the second detection signal 72 falls linearly.
In the conventional rotational angle detecting device having the rotary sensor (that is, the rotation detecting section), as the rotary member (or rotor) rotates, the first to third detection signals are output from the rotation detecting section. When the controlling section detects the rotational direction and rotational angle of the rotary member based on the supplied first to third detection signals, the controlling section detects the rotational direction and the rough rotational angle of the rotary member based on the amplitude (that is, the voltage value) of the third detection signal. In addition, the controlling section detects the very small rotational angle of the rotary member based on the linearly inclined portions of the first and second detection signals. Therefore, the rotational angles and rotational direction of the rotary member can be detected with high precision over wide ranges thereof.
However, in the conventional rotational angle detecting device having the rotation detecting section, the first to third detection signals which are output from the rotation detecting section are used as they are to detect the rotational angles and rotational direction of the rotary member. Therefore, if for any reason a detection signal is erroneously output from the rotation detecting section, a rotational angle and rotational direction corresponding to the content of the erroneously output detection signal is detected. Consequently, erroneous angle detection information is supplied to the controller from the controlling section, so that the controller may not properly control the traction and the suspension of the automobile.
In view of the above-described problems, it is an object of the present invention to provide a highly reliable rotational angle detecting device which can perform a required controlling operation using a detection signal which has been determined as being a proper detection signal by a controlling section which determines whether or not various detection signals output from a rotation detecting section are proper detection signals.
To this end, according to a first aspect of the present invention, there is provided a rotational angle detecting device comprising a rotor connected to a rotary member; a rotation detecting section for outputting a sinusoidal first detection signal and a sinusoidal second detection signal as a result of the rotation of the rotor, the first detection signal and the second detection signal having constant amplitudes, having the same periods, and having wavelengths which are out of phase; a storage section for updating and storing the first detection signal and the second detection signal; and a controlling section. In the rotational angle detecting device, the controlling section compares a most recent first detection signal and a most recent second detection signal output by the rotation detecting section, and determines whether or not either one of the most recent first and second detection signals falls within a proper range with respect to the other of the most recent first and second detection signals. When the controlling section determines that either one of the first and second detection signals falls within the proper range, the controlling section supplies the most recent first and second detection signals to a controller. On the other hand, when the controlling section determines that either one of the most recent first and second detection signals falls outside the proper range with respect to the other of the most recent first and second detection signals, the controlling section does not supply the most recent first and second detection signals to the controller.
In the first structure, the first and second detection signals output from the rotation detecting section are sent to the storage section, are updated, and are stored in the storage section. The controlling section cyclically compares the most recent first and second detection signals output from the rotation detecting section in a determined period. When the controlling section determines that at least one of the most recent first and second detection signals is an unsuitable detection signal, the angle signal based on the unsuitable detection signal is not supplied to the controller. Therefore, an improper piece of detection information which is created based on the unsuitable detection signal is not supplied to the controller, thereby allowing a suitable controlling operation to be performed at all times to operate a fail safe structure by the controller. Consequently, it is possible to provide a highly reliable rotational angle detecting device.
According to a second aspect of the present invention, there is provided a rotational angle detecting device comprising a rotor connected to a rotary member; a rotation detecting section for outputting a sinusoidal first detection signal, a sinusoidal second detection signal, and a third detection signal, the first detection signal and the second detection signal having constant amplitudes, having the same periods, and having wavelengths which are out of phase, and the third detection signal increasing linearly over an entire rotational range of the rotary member; a storage section for updating and storing therein the first detection signal, the second detection signal, and the third detection signal; and a controlling section. In the rotational angle detecting device, the controlling section compares a most recent first detection signal and a most recent second detection signal output from the rotation detecting section, and determines whether or not either one of the most recent first and second detection signals falls within a proper range with respect to the other of the most recent first and second detection signals. When the controlling section determines that either one of the most recent first and second detection signals falls within the proper range, the controlling section compares a most recent third detection signal with the most recent first and second detection signals. When the controlling section determines that the signals fall within proper ranges, the controlling section supplies the most recent first to third detection signals to a controller, whereas, when the controlling section determines that the signals fall outside the proper ranges, the controlling section supplies to the controller the third detection signal previously stored in the storage section and the most recent first and second detection signals.
In the second structure, the first to third detection signals output from the rotation detecting section are sent to the storage section, are updated, and are stored in the storage section. The controlling section, first, cyclically compares the most recent first and second detection signals output from the rotation detecting section in a determined period. When the controlling section determines that both of the most recent first and second detection signals are suitable detection signals, the controlling section cyclically compares the most recent third detection signal output from the rotation detecting section with the most recent first and second detection signals in a similarly determined period. When the controlling section determines that the third detection signal is an unsuitable detection signal, it creates a proper piece of detection information using the most recent first and second detection signals and the immediately previously obtained third detection signal read out from the storage section, and the detection information is supplied to the controller. Therefore, an improper piece of detection information which is created based on any unsuitable detection signal is no longer supplied to the controller, thereby allowing a proper controlling operation to be carried out at all times to operate a fail safe structure by the controller. Consequently, using the detection information based on the first to third detection signals, it is possible to provide a rotational angle detecting device which is more reliable than the rotational angle detecting device having the first structure.
The rotary member may be a steering shaft of an automobile, and the first detection signal and the second detection signal, or the first detection signal to the third detection signal may be steering angle detection signals of the steering shaft.
By virtue of this structure, it is possible to provide a highly reliable rotational angle detecting device for generating detection signals of the steering angle of a steering shaft of an automobile.
The steering angle detection signals may be supplied to the controller through a local area network bus line provided in the automobile.
By virtue of this structure, it is possible to provide a highly reliable rotational angle detecting device for properly performing various automobile controlling operations as a result of generating detection signals of the steering angle of a steering shaft of an automobile.